Head and neck cancer (HNC) compromises approximately 3-5% of all malignancies, causing an estimated 50,000 new cases and over 10,000 reported deaths each year in the US. Despite our improved understanding of the etiology and biology at the molecular level and advances in therapeutics, the 5-year survival rate of HNC only improved marginally to about 57%, with tumor recurrence, metastasis, and resistance to therapy as common causes of treatment failure. The long-term goal of this proposed research is to better understand innate and adaptive immune responses to head and neck cancers for the development of effective immunotherapeutic approaches to combat the deadly disease. Our studies have shown that head and neck squamous cell carcinoma overexpresses human beta-defensin 3 (hBD3), correlating with accumulation of tumor-associated macrophages (TAMs) via the chemokine receptor CCR2. The expression of hBD3 is induced by the activation of epidermal growth factor receptor (EGFR) and the Wnt signaling as well as by inactivation of the tumor suppressor p53; all three pathways are implicated in HNC development. In addition, hBD3 stimulates human macrophages to express tumor-promoting chemokines and cytokines, potentially forming a positive feedback loop driving tumor progression. Importantly, our preliminary data show that HNC-derived hBD3 correlates with accumulation of myeloid-derived suppressor cells (MDSCs). Therefore, we hypothesize that HNC-derived hBD3 functions as an immunomodulator to recruit and activate TAMs and MDSCs, which in turn promote progression of tumors and suppression of anti-tumor immunity. This hypothesis will be tested by two specific aims: 1. Delineate the mechanism by which hBD3 promotes HNC progression through recruitment and activation of tumor-promoting myeloid cells. We will identify signaling pathways and structural features of hBD3 in interaction with TAMs and MDSCs and perform clinical analyses to correlate hBD3 expression with immune responses to HNC in patients. 2. Determine the mechanism by which mBD14, the ortholog of hBD3, promotes tumorigenicity associated with increased TAMs and MDSCs in vivo. We will evaluate the effect of mBD14 on HNC progression and immune responses using an orthotopic mouse model, and then determine the effect of CCR2 blockade and TAM and MDSC depletion on HNC progression in vivo. This proposed research may delineate a new research discovery platform for gene/chemical/immunotherapy interrogation, which will potentially lead to new therapeutic options targeting hBD3 signaling. Evaluation of hBD3 in HNC progression animal models and in HNC patients in association with immune responses is entirely novel. This innovative approach will provide us with new information about immune responses to HNC progression.